| Abstract/Description or Keywords |
During the summer and fall of 2007, Wet’suwet’en Fisheries continued the Moricetown Canyon steelhead tagging program that was initiated in 1999, in coordination with an ongoing coho, sockeye and chinook tagging program. Coho, sockeye and chinook data were analysed separately by Fisheries and Oceans Canada. The data collected for steelhead migration from August to September 2007 are summarized in this report in conjunction with catch per unit effort information summarized by Wet’suwet’en Fisheries. The continued objectives of this steelhead tagging program have been to standardize the sampling methodologies, to evaluate in-season population estimates or indices and to monitor the run timing and relative annual returns of steelhead migrating upstream of Moricetown Canyon. In 2007, 208 steelhead were tagged by beach seining, and 1101 steelhead were captured by dipnetting. The onset of the fishing season in 2007 was delayed substantially due to high water levels. Catch rates indicate that the tagging program encompassed the beginning and peak time of steelhead migration through Moricetown Canyon. However, run timing information from previous years of the study indicate that an early portion of the steelhead run may not have been sampled due to high water levels and consequent late onset of the fishing season. In addition, the late part of the run was not sampled as indicated by the continued catch of steelhead to the last day of fishing on the 29th of September, 2007. A comparison of sex ratios was not conducted because gender identification of steelhead in the fall is notoriously difficult, and has been found to be inconsistent during previous years of the study (1999, 2000 and 2001). Fork lengths for steelhead captured in the beach seine fishery were significantly smaller than for lengths for steelhead captured in the dipnet fishery, similar to findings in 2004 and 2006. The significant difference between fork lengths of fish captured with different gear types this year indicates bias in capture techniques, which further draw the population estimates into question. The number of steelhead tagged in 2007 is considerably lower than the targeted number (600-1,000) for a mark-recapture estimate, assuming a population size between 10,000 and 30,000 steelhead, and recapture rates in 2007 were lower than previous years of the study, with only 0.7 % of the steelhead examined in the dipnet fishery having been tagged by beach seining (8 of 1,101). An additional five recaptures with lower caudal punches but incomplete tag information may have been recaptured from the beach seine fishery in the dipnet fishery, bringing the recaptured rate in 2007 up to 1.2% (13 of 1101). This is the third lowest recapture rate since the initiation of the study, with only 1999 and 2000 having lower recapture rates (0.5% and 0.4% respectively), and is much lower than the highest recapture rate recorded in 2003 at 5.5%. The lower proportion of steelhead recaptures in 2007 is in large part due to the low number of tags applied in the beach seine fishery. In 2007, only 208 tags were applied in the beach seine fishery, the second lower number of tags applied since the initiation of the study, with only 1999 having fewer tags applied be beach seining (165). Eight of the 208 steelhead tagged downstream of the canyon were recaptured in a sample of 1,101 steelhead examined for tags at the canyon. A 5% tag loss was assumed, based on tag loss estimates for beach seine captured steelhead in 2007, and in previous years of the study. The adjusted Petersen estimate for steelhead moving through Moricetown Canyon between August 3rd and September 27th, 2007 based on eight recaptures is 24,316 steelhead (95% confidence interval = 13,746-51,075). It is likely that the five steelhead with lower caudal punches and incomplete tag information, which were captured in the dipnet fishery, are also beach seine recaptures. An alternate Petersen estimate, using 13 recaptures in the sample of 1,101 was calculated as 15,554 (95% CI 9,786-28,475). The 2007 estimates should be viewed in light of constraints of the study, including low recapture rates, incomplete sampling of the steelhead run, nonrandom sampling at the beach seine and dipnet locations, and uncertainties around the number of recaptures in the census sample obtained by dipnetting. |
